DVD (Digital Versatile Disc) and other optical disc recording applications require a semiconductor laser beam with higher optical output to increase recording speed. For example, optical output exceeding 100 mW is desired for gallium nitride based semiconductor laser devices in the 400 nm wavelength band for use in the next generation DVD applications.
Such high output operation involves a large amount of heat generation from the active layer that emits the laser beam. However, the optical output of a semiconductor laser device decreases when it is used in a temperature range above the maximum lasing temperature.
In general, as the temperature of a semiconductor layer increases, its refractive index also increases. Therefore, when a large temperature difference occurs in the waveguide or near the active layer, the refractive index difference within that region increases. This changes optical confinement of the horizontal transverse mode in particular, and thereby higher order modes are more likely to occur.
Furthermore, in high output operation, higher order modes are more likely to occur in the horizontal transverse mode as the operating current increases. This may result in a kink phenomenon in the characteristics of optical output versus operating current. This phenomenon is undesirable because it restricts the available range of optical output of the semiconductor laser device.
A previously disclosed technology (U.S. Pat. No. 6,775,311) involves stabilization of the horizontal transverse mode in an attempt to remedy the above problems. In this disclosed technology, a hollow portion is provided approximately parallel to the ridge waveguide in the current blocking layer.